1. Field of the Invention
The present invention relates to a piezoelectric fan. More specifically, the present invention relates to a piezeoelectric fan using a bending vibrator such as a bimorph vibrator.
2. Description of the Prior Art
The conventional piezoelectric fan which is the background of the present invention is disclosed, for example, in the specification of the U.S. Pat. No. 4,498,851. The piezoelectric fan disclosed in this U.S. patent has a bimorph vibrator having a cantilever structure, being driven by a drive circuit of separated excitation type.
In such a conventional piezoelectric fan, a supporting part of the cantilever is required to be fixed in an ideal manner, but practically, the supporting part is usually formed integrally in one-piece with a case, and is fastened by bolts or fixed by an adhesive to this case. The mass of such a case is finite, and accordingly the supporting part and the case whereon it is mounted vibrate. Not only is this vibration transmitted to the equipment whereon the piezoelectric fan is mounted, and exerts an adverse effect on the equipment, but also the amplitude at the tip of an elastic blade is reduced by vibration of the supporting part, resulting in a reduction in the quantity or speed of the wind. Accordingly, the conventional piezoelectric fan having a cantilever structure is not so good in efficiency.
Also, the conventional piezoelectric fan is driven by the drive circuit of separated excitation type, and therefore the drive circuit cannot respond to the resonance frequency, as oscillation of the vibrating part becomes unstable. This results in a reduction in the wind quantity when the resonance frequency of the vibrating part is varied. Variation of the resonance frequency may be caused by an environmental change such as a temperature change, a change with time or the like, or by an adhesion of, for example, adhesive material to the blade attached to the tip of the vibrator. In the conventional piezoelectric fan, when the resonance frequency is varied, readjustment is required to coincide the resonance frequency with the driving frequency. However, practically such a readjustment is very difficult to make.